Heater



Dec. 16, 1958 I 2,864,929

HEATER Filed March 14, 1957 INVENTOR.

%%wem United States Patent HEATER Application March 14,1957, Serial No.645,947 3 Claims. (Cl. 219-19) This invention relates to a heater unitfor use in coffee makers or similar devices where an electrically heatedimmersion unit is desired.

In the provision of heating means for electrically heating a liquid,'itis necessary to isolate the electricity-conducting elements from theliquid. Heat transfer varies inversely with distance spacing the heatingconductor and the liquid to be heated, so that, forrapid heat transfer,the heating element should be close to the liquid.

However, proximity of the heating conductor to a metallic surfaceseparating the liquid from the heating element is conducive of dangerousshorts in the electric circuit and where such elements arerelativelyclose together means must be provided to prevent such accidents.

l It is anobject of the present invention to provide a heating unit inwhich the heating element is close to the liquid to be heated but iswell sealed and insulated electrically therefrom.

It is another object to provide an insulating structure which will havesubstantially the same coefiicient of expansion as the heating elements.

Another object is to achieve uniform spacing of the conductive parts ofthe heating unit from the metal enclosure.

Still another object is to provide a heater in which the conductiveresistance unit is surrounded by a non-hygroscopic insulating materialhaving high electrical resistance and high heat conductivity.

Further objects are to provide a compact heater having long life, toprovide a construction which will facilitate manufacture and to providehigh heating efiiciency.

These and other objects will appear from the following description andthe accompanying drawings.

Of the drawings:

Fig. 1 is an axial sectional view of a heater constructed in accordancewith and embodying the invention;

Fig. 2 is a perspective side view of the tubular ceramic core with theresistance wire winding, the anchor clips and wire leads attachedthereto; and

Fig. 3 is a perspective view of the insulating disc partly broken awayand partly in section.

Referring to the drawings, the heater includes a cylindrical tubularbody of ceramic insulating material formed with an axially open notch 11at one end and a similar oppositely open notch 12 at the opposite end ofthe body. The notches 11 and 12 may be diametrically opposed as shown inthe drawing, or preferably, are arcuately separated by about 90 to makethe wire leads lie closer together as hereinafter described.

Clamped to the ceramic body within each notch is a metal anchor clip 13,14 respectively, the notch and the clip being of such dimensions as toprovide communication from the interior of the tubular body to theoutside thereof through said notches when the anchor clips are in place.The clips are of the type shown and described in my copendingapplication Ser. No. 609,595, filed September 13, 1956, and entitledClip. The clips are of inconel metal of soft spring properties.

2,864,929 Patented Dec. 16, 1958 Theheating element 15 is of nichromewire preferably of round cross-section and is wound in a helix of spacedapart turns from one of the clips to the other, the ends of the heatingelement being spot-welded to the clips 13, 14.

In securing the wire heating element to the clips 13, 14, it isdesirable to provide some yieldability in the connection. For thisreason, the clips 13, 14 are formed each with a pair of spaced apartanchoring horns 13a and 13b, spaced from each other circumferentially ofthe ceramic support and each end of the resistance wire is passed aroundone of the horns and reversely about the other to which it is welded,the bowed condition of the wire between the horns provides sufiicientslack to prevent breaking of the wire at the weld, all as morespecifically illustrated and described in the aforesaid application.

Wire leads 16, 17 of stranded nickel wire insulated with asbestos andglass braid are secured to the anchor clips 13, 14 respectively andextend through the bore of the body 10 and through a perforated disc 18of steotite, or other insulating material, the lead wires being secured'to the anchor clips by crimping a portion of the clip thereto as at 19,20 and may be additionally secured'by welding to provide a continuousconductive path from one lead wire to another in which all of the metalparts are of corrosion resisting material.

The disc 18 is considerably larger in diameter than the tubular core 10and may have a pair of spaced apart openings 21, 22 therethrough, whichmay be spaced radially of the center of the disc to receive the wireleads 16, 17. These openings may be optionally surrounded by tubularraised collars 23, 24 on the side of the disc away from the core 10.

The tubular core 10 with the heating element thereabout is surrounded bya metal case 27 of cup-like construction usually of aluminum, the wallsof the case adjacent the resistance wire being spaced radially from theheating element'and the conductive clip being spaced axially from thebottom of the case by the end of the core 10 extending beyond the clipand into an end portion 28 of the case of reduced diameter for centeringthe core.

The disc 18 rests upon the opposite end of the core tube 10 andinsulates the clip 13 from the metal case 27, the core tube 10preferably but not necessarily being centered by a shoulder 37 engagingin the end of the core tube.

To provide against shorting of the heating unit due to expansion of theheating wire into contact with the case and to prevent shifting of theconvolutions of wire 15 on the core tube, a solid filling 30 ofinsulating material is provided about the core 10 within the case. Thisfilling is of substantially the same coefiicient of expansion as thesurrounding material and preferably comprises a solidified body ofmagnesium phosphate formed in place. The material for forming thefilling 30 may be introduced into the case 27 between the case and thecore 10 in liquid state or as a powder and ordinarily flows through slot11 soas to provide a layer 31 across the bottom of the case. One mannerof positioning or obtaining solidified magnesium phosphate in theposition described is disclosed and claimed in copending applicationSer. No. 628,272, filed December 14, 1956, and entitled Method of MakingElectrically Insulated Heating Units. The magnesium phosphate adhesivelyadheres (without chemical reaction or fusion) to the ceramic tube andthe aluminum case and the nichrome wire.

Completing the assembly of the heater are suitable means for holding thedisc 18 in the case 27 and these comprise, in the form of the inventionillustrated, a layer of sealing material 25, such as ceramic cement,which is 3 poured in place as shown and which sets up to seal the end ofthe heater.

The heater unit is adapted to be mounted, for example, in a cofifeemaker. In't'ne embodiment illustrated, the case 27 is formed Withacircular shoulder 35, as by folding a portion of the case on itselfduring theforming operation, which shoulder abuts against one side ofthe plate 34. The end of the case is externally threaded at 36 toreceive a nut 38 which can be screwed on and tightened down in placeagainst the other side of plate 34.

The objects of the invention are thus obtained by the provision of aheater having very low electric leakage characteristics, extremelyexcellent life (due to the very rigid placement and holding of theheater wire), but retaining relative inexpensiveness and ease ofconstruction.

While one embodiment of the invention has been shown and described forillustrative purposes, it will be apparent to those skilled in the artthat various changes andmodifications may be made therein withoutdeparting from the spirit or scope of the invention as it is defined bythe following claims.

I claim:

1. A heater for an appliance, said heater comprising a cylindricaltubular core of ceramic material having axial notches in its oppositeends, an anchor clip engaged in each notch, a resistance wire elementextending helically about said core from one anchor clip to the other inopen spaced coils, said element being welded to said clips, a disc ofinsulating material of larger diameter than the tubular core, said discbeing mounted over one end of the core, lead wires connected to saidanchor clips and extending through openingsin the disc, a cup-like caseof aluminum enclosing said tubular core and said I 4 disc, a cylindricalbody of solidified magnesium phosphate filling the space between thecase and the core and providing a solid enclosure-of insulating materialsurrounding the resistance wire element, said body of magnesiumphosphate also forming a cover layer extending across the bore of theinner end of said core, said case having a reduced diameter portion atits closed end engaging the inner end of thecore to center it, said dischaving a shouldered portion engaging with the other end of the core tocenter it, and sealing means between the disc and the case-and sealingthe lead wires in the openings in said disc.

2. A heater as in claiml wherein said body of magnesium phosphateextends through one of the notches in said core.

3. A heater as in claim 1 wherein the end portions of said wire elementare reversely bent around said anchor clips, anexternal shoulder isprovided on said case with the end of the case beyond the shoulder beingthreaded, and a nut engaging the threaded end of, said case.

References Cited in'the file of this patent UNITED STATES PATENTS

